[wrap_comments] Backtick causes parsing error

[otavio]

Using backtick inside a quoting block, even if marked as text, causes a parsing error.

Example:

/// Simple block
///
/// ```text
///  `
/// ```
fn main() {
    println!("Hello, world!");
}

It has been found while trying to reduce the test case for #3008. The use case is we did a small ASCII diagram and triggered a 101 return code, while led to this test.